Steam cycle in which more than two stages of feed water heating are carried out by one exhaust steam system from auxiliary turbine



March 16, 1965 YASUO TAKEDA 3,173,267

STEAM CYCLE IN WHICH MORE THAN TWO STAGES OF FEED WATER HEATING ARE CARRIED OUT BY ONE EXHAUST STEAM SYSTEM FROM AUXILIARY TURBINE Filed April :5. 1964 INVENTOR. yasu o 7}; 9/ 4 United States Patent 3,173,267 STEAM CYCLE IN WHICH MORE THAN TWO STAGES OF FEED WATER HEATING ARE CARRIED OUT BY ONE EXHAUST STEAM SYSTEM FROM AUXILIARY TINE Yasuo Takeda, Tammi-kn, Kobe-shi, Hyogo-lren, Japan, assignor to Kawasaki Jukogyo Kahushiki Keisha, Hyogo-ken, Japan, a corporation of Japan Filed Apr. 3, 1964, Ser. No. 357,242 Claims priority, application Japan, Apr. 10, 1963, 18,876/ 63 1 Claim. Cl. (60-67) The present invention relates to a steam cycle which has an auxiliary turbine or turbines besides a main turbine, and exhaust steam of the former is led into feed water heaters to condense itself and heat the feed water from the main turbine.

In the prior art, exhaust steam from such an auxiliary turbine or turbines has been led directly into a single feed Water heater to be condensed therein. In this art, even the exhaust steam of the auxiliary turbine is in state of superheated condition, it can only heat the feed water up to nearly a saturated temperature corresponding to its pressure, in spite of that exhaust steam is capable of heating the feed water up to higher temperature.

In order to overcome this disadvantage, according to the present invention, an exhaust steam from said auxiliary turbine is first led into a preliminary feed heater to exchange its sensible heat with the feed water at higher temperature thus lowering its temperature and enthalpy in some degree and thereafter introduced into a secondary feed heater, which is placed in lower temperature side of feed water from the primary heater, to exchange its remaining heat and then condense therein.

An object of the present invention is to improve a thermal efliciency of an ordinary feed heating cycle of a plant comprising a main and auxiliary steam turbine by making said cycle closer to an ideal Carnot cycle.

One embodiment according to the present invention will be described hereinafter by way of an example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a steam cycle showing a conventional system wherein exhaust steam from an auxiliary steam turbine is led into and condensed in a feed water heater for the main turbine;

FIG. 2 is a schematic diagram of a steam cycle showing one embodiment according to the present invention; and

FIG. 3 is an enthalpy-entropy-diagram showing expansion lines for a main and auxiliary turbine.

With reference to FIG. 1, steam generated in a boiler 1 is led into a main turbine 2 and an auxiliary turbine 21, exhaust steam from said main turbine 2 is condensed in a condenser 3, thus produced condensate will pass through a first, second and third stage feed heater 5, 6, 7 via a condensate pump 4 so as to be heated therein and then pass through a fourth and fifth stage feed heater 2 10 via a feed pump 8 so as to be heated therein and thereafter enter said boiler 1.

Extracted steam from the main turbine 2 will enter each stage feed water heater through each stage bleeder pipe 11, 12, 13, 14, and exchange its heat with the feed water and condense therein, thus produced drain will flow successively itno a feed water heater of lower temperature side through a drain connecting pipe 16, 17, 18, 19, 2t and join together and as a whole enter said condenser 3 finally. And an exhaust steam from an auxiliary turbine 21 (for instance a turbine for the feed water pump) will join with third stage extracted steam in a third stage bleeder pipe 13 via a bleeder pipe 22 and then enter a third stage feed water heater 7 and condense therein.

3,173,267 Patented Mar. 16, 1965 According to the present invention, it is contemplated to make a conventional feed water heating cycle closer to an ideal Carnot cycle thereby to improve a thermal efficiency thereof. One embodiment of a cycle according to the present invention is shown in FIG. 2, in which a five stage feed water heating system is illustrated similarly to FIG. 1 for simplicity comparison. Machineries and devices common to both systems are designated by similar reference numerals. A cycle according to the present invention as illustrated in FIG. 2 differs from. a heretofore known cycle as illustrated in FIG. 1 only in that an exhaust steam from an auxiliary turbine 21 (such as a turbine for feed pump) will pass through a preliminary exhaust feed heater 23 provided between the fourth and fifth stage bleeder feed heater and then enter a third stage feed heater 7 in the former cycle. Arrangement of other system and flow of steam and water are quite identical in both cycles. Therefore, it is not necessary to repeat description given in connection with FIG. 2.

Now, a reference will be made on an embodiment as shown in FIG. 2 to describe a reason why said preliminary exhaust feed heater 23 does contribute to improve a thermal elficiency.

FIG. 3 is an enthalpy-entropy-diagram showing expansion lines for the main and auxiliary turbine. By a line I is designated a saturation curve, II an expansion line of a main turbine and III that of an auxiliary turbine respectively. And by P P P P P is designated a constant pressure curve respectively, by i t t r 1 r a constant temperature curve respectively.

Each reference mark denotes following things:

Pressure, temperature and enthalpy at the entnance of the main and auxiliary turbine P t Pressure, temperature and enthalpy at No. 5

bleeder point of the main turbine P t Pressure, temperature and enthalpy at No. 4

bleeder point of the main turbine P t Pressure, temperature and enthalpy at No. 3

bleeder point of the main turbine P t Pressure, temperature, enthalpy at the outlet of an auxiliary turbine P t i A saturated temperature corresponding to a pressure P at No. 5 bleeder point (a tempera,-

ture of feed water at outlet of fifth feed heater) M. A saturated temperature corresponding to a pressure P, at No. 4 bleeder point (a temperature of feed water at outlet of fourth feed heater) A saturated temperature corresponding to a pressure P at No. 3 bleeder point (a temperature of feed water at outlet of third feed heater) Since an auxiliary turbine is smaller and normally of simpler construction than a main turbine, an internal efliciency of the former is less than that of the latter. Accordingly, as shown in FIG. 3, an expansion line III of an auxiliary turbine will become closer to a horizontal than that of a main turbine. Temperature and enthalpy at its outlet t i will become greater than those at the corresponding point of a main turbine, that is, temperature and enthalpy at No. 3 bleeder point t;,, i A temperature t is not only sutficiently higher than that t of feed water at the outlet of a feed heater (third stage heater in FIG. 2) in which an exhaust steam from the auxiliary turbine will exchange finally its heat and then condense, but also becomes normally higher than those r r at the outlet of higher stage feed heater (a fourth, fifth feed heater in FIG. 2). That is, exhaust steam from an auxiliary turbine is capable of heating the feed water discharged from the feed heaters of higher stage than the one in which said exhaust steam is condensed.

In a conventional cycle (FIG. 1), this exhaust steam from an auxiliary turbine of high temperature and high enthalpy exchanges its heat in a single feed water heater (third stage feed heater in FIG. 1) and condenses therein despite the fact that said steam is capable of heating the feed water at higher temperature. However, in a cycle according to the present invention (FIG. 2), exhaust steam from an auxiliary turbine will exchange its heat with the feed water at a higher temperature in a preliminary feed heater (by exhaust steam) thus lowering its temperature and enthalpy in some degree and thereafter enter a third stage feed heater to exchange its remaining heat and then condense therein.

According to a principle of thermodynamics, if a heat exchanging process is carried out in a condition of small temperature difiference between a heating and a heated substance in a thermodynamical cycle, an increasing rate of entropy in said process will be reduced thereby a thermal efliciency of the cycle is improved. That is, it is evident for this reason that a thermal efiiciency is more improved in a cycle according to the present invention (FIG. 2) than in a conventional cycle. And it can be easily understood by carrying out some actual heat calculations.

A cycle comprising a preliminary feed water heater according to the present invention contributes to improve not only an efiiciency but also manoeuvrability of the system. That is, a capacity of a feed waterheater (a third stage feed heater in FIG. 1), in which exhaust steam from an auxiliary turbine will condense, may become insufficient and thereby a part of exhaust steam has to be discharged outwardly by some means in case of starting or a lower loading of "a turbine cycle as shown in FIG. 1 because the feed water is reduced relatively to an exhaust steam from an auxiliary turbine. However, a preliminary feed heater will compensate for a capacity 4 shortage of said condensing f eed heater and considerably alleviate the situation in a cycle provided with said preliminary feed heater as shown in FIG. 2.

What is claimed is:

A steam turbine system having a main turbine, an auxiliary turbine, boiler means for feeding steam to said main turbine and said auxiliary turbine, a first group of condensing feed heaters, means for feeding steam from said main turbine to said first group of condensing feed heaters, and the first group of feed heaters operating at a first temperature and pressure, a second group of feed heaters, means for conveying steam from said main turbine to said second group of feed heaters, said second group of feed heaters operating at a higher temperature and pressure than that of said first group of condensing feed heaters, a preliminary exhaust feed heater connected in series with the feed heaters of said second group of feed heaters, means for conveying exhaust steam from said auxiliary turbine to said preliminary exhaust feed heater, whereby said exhaust steam will condense therein and will exchange a part of its heat with the feed water therein, and means 'for conveying exhaust steam from said preliminary exhaust feed heater to said first group of said condensing feed water heaters, a condenser, means for conveying exhaust steam from said main turbine to said condenser and means for conveying condensate from said condenser to said first group of condensing feed heaters, and means for conveying condensate from said second group of feed heaters to said boiler.

References Cited by the Examiner UNITED STATES PATENTS 3,083,536 4/63 Vogler 6067 X 9/53 Heller 6067 X 

